Electric-circuit element



y 1942. w. L. BARROW I 2,281,550

ELECTRIC CIRQUII' ELEMENT:

Filed Aug. 14, 1937 2 Sheets-Sheet l May 5, H542.

W. L. BARROW ELEGTRICCIRCUIT ELEMENT Filed Aug. 14, 1937 2 Sheets-Sheet 2 WiZwzer Marrow Patented May 5, 1942s 2,281,550 ELEcTaIc-cmcurr m Wilmer Lanier Barrow, Newton, Mass, asslgnor corporation of New York to Research Corporation, New York N. Y., a

Application August 14, 1937, Serial No. 159,031

28 Claims.

' The present invention relates to electric-circuit elements and, more particularly, tocircuit elements for use with electromagnetic waves of extremely high frequencies.

As explained in my paper, entitled, Transmis sion of Electromagnetic Waves in Hollow Tubes of Metal, Proceedings of the Institute of Radio Engineers, October, 1936, pp. 1298 to 1328, it is possible to transmit ultra-high-frequency electric energy through the interior of a hollow conducting pipe or tube.

There is a minimum or critical frequency for each type of wave below which it cannot exist in, and, cannot be transmitted through, the hollow pipe. This critical frequency is diiferent for each type of wave and for different pipe materials, shapes and cross-dimensions. As given on page 1323 of my said paper, for a pipe of circular cross section, the minimum frequency In below which no transmission can take place by any type of wave is:

and 1r:3.1416.

The value f0, however, applies to a particular wave. Each type of wave has its own critical frequency.

For air-filled pipes, this formula becomes \=3.41a, where A is the wave length corresponding to the frequency f0.

The type of wave that is possible if the frequency equals or exceeds by a slight amount the value of in given by this formula may be referred to as the first-order transverse wave. As the frequency is raised above this value, other types of waves are possible, each of which has its own critical frequency. The type of wave having the second-lowest critical frequency, for example, may be referred to as the zero-order longitudinal wave. It can exist only if the frequency equals or exceeds the frequency given by the same Y 7 formula, except that the constant 1.841 is re-v placed by 2.405, a circular cross-sectional pipe being again referred to.

Other types of waves have successively higher values for their critical frequencies. Although there is a very large number of these wave types, the first several types are at the present time of the most practical application for reasonably small pipe diameters.

An object of the present invention is to provide a novel high-frequency low-loss impedance element.

A further object is to provide a novel system comprising a hollow chamber or cavity that may have sharp resonance characteristics at a predetermined frequency or frequencies, for use as a circuitelement, either with hollow-pipe systems of the above-described character or with circuits of the conventional kind or any other kind. Energy may be taken from or supplied to the novel circuit element of the present invention, which may be used for transmission or reception over hollow-pipe systems of the above-described character, and also for other purposes.

Other and further objects will be explained hereinafter and will be particularly pointed out in the appended claims.

The invention will now be explained more fully in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic view of a vacuum-tube oscillator embodying a cylindrical circuit element in accordance with the present invention, the circuit element being shown in perspective and longitudinal section; Fig-.2

is a similar view of a modification; Fig. 3 is a section of a spherical circuit element embodying the invention; Figs. 4, 5 and 6 are longitudinal sections similar to Figs. 1 and 2 of -modified circuit elements, such as may constitute terminal devices for connection in hollow-pipe and conventional circuits for use at ultra-high frequencies; Figs. 7, 8 and 9 are perspectives of modified circuit elements adapted for use with waves of the transverse type; Figs. 10 andll are sections similar to Fig. 3 of modified circuit elements; Fig. 12 is a section similar to Fig. 5 of a further modification; and Fig. 13 is a perspective of still another modification, embodying a circuit element that is rectangular in cross section.

The hollow cavity is indicated at 51 in Figs. 1, 2 and 4, at 63 in Figs. 5 and 12, at 15 in Fig. 6, at in Figs. 7 and 9, at 46 in Fig. 8, at I22 in Figs. 3, 10 and 11, and at H8 in Fig. 13. At least its inner wall or surface is of metal, such as copper or aluminum, or is otherwise rendered conducting; though the wall may be constituted of a thin dielectric the outer surface of which may be rendered conducting in any desired way, as by depositing a metal coating thereon. For illustrative purposes, this is shown in Fig. 3, the dielectric support being shown at I1 and the metal deposit at I8. All such constructions or their equivalents will be included in the term "inner conducting wall" or surface" of a pipe or tube, or conducting cavity," or their equivalents. As materials of high-dielectric constant, such as liquids and solids, introduce losses that may render the device extremely inefiicient as a circuit element, it is preferred that the space in the cavity contain some low-loss non-conducting dielectric, such as air or other gas, or the chamber may be evacuated.

In Figs. 1, 2, 4 to 9 and 12, the hollow cavity is shown in the form of a closed'metal cylindrical hollow-pipe chamber 51. Hollow cavities or chambers or shells of any cross-sectional shape, such as rectangular, square or ellipsoidal, are, however, included within the present invention, as are also three-dimensional or space cavities of various geometrical shapes, such as cylindrical, spheroidal, ellipsoidal, rectangular or parallelopiped. The spheroidal shape is illustrated at I22 in Figs. 3, 10 and 11. A hollow-box shape, or a cylindrical shape of rectangular cross section, is illustrated in Fig. 13 at I18.

If the energy becomes wastefully dissipated from the chamber, it can not, of course, have very much effectiveness as a circuit element. To reduce losses, therefore, the chamber should be substantially closed to prevent radiation of radiofrequency energy therefrom. Where it is desired to operate the circuit element at resonance, so as to enhance its operation, it should be properly shaped and dimensioned to produce space resonance of the electromagnetic waves within the cavity, at the frequency of operation; the dimensions of the shell should then, for example, be about equal to or greater than one half of the free-space wave-length of the oscillations in the non-conducting space. The radius of the sphere I22 of Figs. 3, 10 and 11, for example, may be about equal to one fourth the wave-length. Other sizes of radii may also be employed, but the phenomenon is critical, as the resonance is very sharp. It is not necessary, however, that the chamber be operated at resonance. On one side of resonance, the impedance of the chamber will be inductive; and on the other side, capacitive.

One end of the tube chamber 51 may be wholly closed, as illustrated in Figs. 2 and 4, by means of a flat metal wall Ii, shown in the form of an end plate or disc. A very simple form of cavity may thus be provided, suitable for use as a circuit element. It may, for example, be connected to a hollow pipe system in any desired way, as by means of a pipe 43, illustrated in Fig. 4, disposed at an intermediate point in the side of the chamber 51. The cavity 51 may, however, be connected to a hollow-pipe system at other positions than as illustrated at 43 in Fig. 4.

The ideal toward the attainment of an effective circuit element, as before explained, is completely to close the chamber. This ideal, however, is altogether impossible of attainment, for useful purposes; because, since the energy can not be taken out of a completely closed chamber, it could not then be utilized at all. An opening must be provided in the circuit element through which to extract the energy. Such an opening is shown at 1, disposed centrally of the smooth metal plate 8 of Fig. l, for example, and through which a conducting exciting rod 58 is permitted to enter the chamber. The rod 55 is shown supported axially in, and spaced from the walls of, a tubular conducting section SI of the chamber 51 by insulating members 8. Corresponding insulating members I may be employed in the other fi ures, though not always illustrated herein, .for clearness. One end of the conductor 58 extends axially into the chamber 51 for a short distance through the opening 1. The rod 58 constitutes the inner section, and the tubular portion GI the outer section, of a coaxial or concentric-tube section or line. Communication may be effected between the chamber 51 and the tubular section 6| through the opening 1 by means of conductors 3 and 62, one connected to the tube section BI and the other to the conducting exciting rod 58. A connection is thus provided between the two conductors of the bi-conductor system 3, 62 and the chamber 51. In some cases, however, the lead or leads to the rod 58 and related apparatus may be brought into the pipe through what corresponds to the tubular section GI and the opening 1. In Figs. 3, l0 and-11, for example, conductors I24 connect a rod I2I, corresponding to the rod 58, and a tubular section I25, corresponding to the tubular section H.

The presence of the opening 1, of course, prevents the chamber of the novel circuit element from being wholly closed; and the same is true where more than one opening is provided in the chamber as, for example, in connection with the circuit element illustrated in Figs. 7, 8, 9 and 12. The presence of such opening or openings, however, is essential, as before stated, in order to make it possible to connect the chamber with an external high-frequency circuit or circuits, in operative relationship, connections to the circuit or circuits being made at the opening or openings. A compromise has 'to be effected between the theoretically completely closed chamber that prevents radiation losses because of its complete closure and the necessity for providing an opening or openings in order to obtain access to the chamber. The opening or openings shouldv be small enough, therefore, to reduce radiation losses from the chamber substantially to a minimum. The means for connecting the circuit element to the circuit or circuits, furthermore, should be designed, as illustrated in Figs. 1 and 2, for example, so as to guide electromagnetic energy between the chamber and the circuit or circuits with low loss. Where energy is transferred through the opening or openings into the chamber from outside space, or into outside space from the chamber, great losses are encountered. An approach is thus provided toward the ideal of a substantially completely closed chamber, providing a very eflicient circuit element in which the energy is substantially completely enclosed and from which, therefore, a minimum of energy becomes dissipated by radiation.

Where a single opening 1 is provided, the chamber constitutes a self-impedance. Where a plurality of openings is provided, the chamber may constitute a mutual impedance, common to two or more circuits to which the chamber is connected at the openings.

If it is desired to retain the wholly closed nature of the wall 6 in connection with the twoconductor system 3, 52, this may be effected as illustrated, for example, in Fig. 2. Instead of the tubular section 6| in the end wall 6, a corresponding tubular section 3| may be disposed along an opening 21 at an intermediate point in the side wall of the chamber 51. An exciting conductor rod 33, at right angles to, and opening freely into, the chamber 51, along the opening 21, corresponding to the exciting rod 58 of Fig. 1, may extend axially through the tube 3|. This modification may be particularly advantageous in the event that it is desired to have the rod 33 contact with the wall of the chamber 51, as shown at 2|. The exciting rod 33 may form the inner element of a coaxial or concentric-line connection, the outer element of which is constituted of the tube 3|. 3|, 33 is of the same nature as the coaxial connection 58, SI of Fig. 1, except that the exciting rod 33, as before stated, makes contact at its free end 2| with the chamber 51.

A similar construction is illustrated in Figs. 5 and 12. The exciting rod 64 extends axially through a tube 65 that is disposed at right angles to, and opens freely into, the chamber 63, along an opening 56, at an intermediate point thereof. As in the case of the rod 33, the free end of the rod 64 is shown making contact with the chamber 63 at 2|. In Fig. 11, similarly, the rod |2| is bent into contact with the sphere I22 at 2|. Although illustrated as making contact at 2|, it is not essential that the rod 33 or 64 touch the wall of the chamber 63 at 2|; as illustrated in Fig. 3, it may be inserted in the cavity without actually touching the wall, with almost equal effectiveness, whereno conductive path between the conductors 62 and 3 is desired.

The tube conductor 65 and the rod 64 of Figs. 5 and 12 constitute a coaxial or concentric-tube connection, of the same nature as the connection 58, 6| or 3|, 33. The rod 64 and the tube 65 of this coaxial or concentric tube system are connected by terminal conductors 56 that correspond to the conductors 3, 62 of Figs. 1 and 2. A connection is thus provided between the twoconductor system 66 and the chamber 63, at an intermediate point of the chamber 63, by means of the exciting rod 64 projecting through. the opening 56 in the wall of the chamber 57, in the same way as described in connection with Fig. 2.

As the two conductors 3 and 62 may be connected into a circuit of conventional or other type, for example, the vacuum-tube oscillator 53 of Figs. 1 and 2, a two-conductor circuit element which may have marked resonant properties is thus provided. When the novel circuit element is used in connection with hollow-pipe systems, however, it is not necessary to provide it with the two conductors 3 and 62, because of the uniconducting nature of hollow pipes. The apparatus illustrated in Fig. 4, therefore, is more particularly adapted for use with hollow-pipe systems.

The elements 58, 6| and related parts may be referred to as a terminal device. The various types of waves before referred to may be separately excited by particular kinds of terminal devices. Terminal devices for longitudinal waves are fundamentally difierent in construction from those for transverse waves. Or. the frequency and the configuration of the terminal device depends the shape of the lines of electric and magnetic force into which may be resolved the electromagnetic wave that is transmitted down the pipe. The configuration of the The coaxial connectionwave that is to be. excited determines, therefore, the design of the terminal. By having the conducting rod 58 axially positioned, as above described, it may coincide with a line of electric intensity for the longitudinal wave. The beforedescribed transverse disposition of the rod, on the other hand, causes the standing waves within the cavity to have diflerent configurations from those present with a longitudinal disposition, as in Fig. 1. The resonant frequencies and other electrical behaviours of the elements are slightly different, but in each case sharp resonant properties may be exhibited.

The value of the impedance, whether induc-' tive or capacitive, of the circuit element of the present invention may be varied or tuned 'over a wide range through adjustment of an adjustable terminator, such as a metal or other conducting plunger or piston 53, 61, 68 or 14 that is fitted snugly in a length of the hollow-pipe chamber 51 of the terminal device. The adjustment of the plunger or piston 59 may be effected by means of an adjusting rod 60. In Fig. 5, two such plungers 61 and 68 are illustrated, at both ends of the hollow-pipe chamber 63, adjustable by means of respective adjusting rods 10 and 69; and in Fig. 6, the plunger 14 is csimilarly adjusted by means of the adjusting ro The resonant chamber or cavity 51 of Figs. 1, 2 and 4, between the wall 6 and the adjustable piston or plunger 59, is thus rendered adjustable or tunable for tuning purposes, to vary its characteristics, and thus to modify or alter the characteristics of the main hollow pipe 43 or other electric system to which it may be connected. The wall 6 and the piston 59 prevent an exchange of energy between the inside and the outside of thechamber 51, and act also to increase the effectiveness of the device, over a band of frequencies, by reflecting radiation that is propagated in the hollow chamber 51.

At a certain setting or settings of the plunger 59 of the novel two-conductor circuit element shown in Figs. 1 and 2, and the novel hollowpipe circuit element shown in Fig. 4, for example, standing waves will thus be produced in the hollow cylindrical chamber between the wall 6 of the hollow cavity 51 and the plunger 59. These standing waves in the closed resonant chamber or cavity 5! will produce therein a condition of space resonance that will be reflected as a change in the apparent impedance at the connections 3, 62 that, for example, connect the chamber 51 with the oscillator 53 of Figs. 1 and 2. This, in turn, will produce a reaction on the oscillator 53 or other source of energy or other electric circuit to which the concentric line 58, 6| or 33, 3| is connected. The consequent changes in plate and grid currents may be observed with the aid of any suitable indicating instrument.

The purpose of the piston is to provide an easy method of tuning or adjusting, but the chamber may be previously designed so as to be resonant without such subsequent adjustment.

The circuit element of this invention is attended by very low losses and with correspondmgly high impedance. By virtue of the fact that there can be no radiation from the chamher, in the first place, the customary radiation losses of open systems do not occur with this device. The absence, with the use of this chamber, of the supporting insulators necessary to be employed with conventional circuit elements likewise does away with losses from that source.

The conduction-current losses in the metal of the resonant circuit element, finally, are relatively small because of the large conducting surface provided by the walls of the cavity. By appropriately modifying the shape of the cavity, as hereinafter described, a minimum of losses may be realized under different conditions of application.

As the energy should be delivered by the conductors 3, 52 to the chamber 51 with an eificiency depending upon the results desired, consistent with the very high frequencies employed,

the component parts of the terminal device should have such dimensions, and should be so designed,ias to obtain a maximum energy transfer, at a particular frequency, from the terminal conductors 3, 52 to the chamber 51, under normal operating conditions; or a uniform energy transfer over a band of frequencies; or to attain some other end.

A resonant hollow-cavity circuit element is thus provided by the present invention, which may be used for many purposes, both at and away from resonance. It may, for example, be embodied in any appropriate ultra-high-frequency generating, stabilizing, choking, amplifying, controlling, modulating or demodulating equipment of any well known character. As an example, it is illustrated in Figs. 1 and 2 as embodied in regenerative resonant-cavity vacuumtube oscillators that may be used as sources of electromagnetic energy of ultra-high frequency.

The oscillator 53 of Figs. 1 and 2 may comprise a vacuum tube diagrammatically shown as provided with a cathode 55, a grid 52 and an anode or plate 54. The plate or output circuit, between the cathode 55 and the plate 54, is illustrated in Fig. l as embodying a tuned circuit comprising a coil 49 shunted by a tuning condenser 41, and containing also a' plate battery or other source of energy 50 that may be shunted by a by-pass condenser 45.

The circuit element of the: present invention is shown in Fig. 1 connected, by the two conductors 3 and 52 of the bi-conductor circuit, in the input circuit, between the cathode 55 and the grid 52, shunted by a biasing resistor 5|. In Fig. 2, the resistor 5| is shown replaced by a parallel-connected coil 4| andadjustable condenser 39. It may be desirable to connect an impedance 31, shunted by a condenser 35, in the cathode leads common to the input and output circuits, as illustrated in Fig. 2, where the circuit element is shown connected in the plate or output circuit of the tube, between the filament 55 and the plate 54, in substitution for the tuned circuit 41, of Fig. l. The exciting rod 33 is shown connected to the plate 54 by the conductor 62; and the tube 3| is shown connected to the filament 55, through the battery 50, by the conductor 3.

The circuit element of the present invention may be connected also in any other desired part of the oscillator circuit. In all cases, the energy may be assumed to be taken from the vacuumtube apparatus 53, and delivered to the chamber 51, and from the chamber 51 to the vacuum-tube apparatus 53, by means of the output terminal conductors or leads 3 and 62 and the terminal device 58, 6|.

Assuming the parameters of the oscillator system to be suitably selected and adjusted, as by means of the tuning condensers 33 and 41 and the plunger 53, the system will oscillate under the control of the novel circuit element oi the present invention.

A high degree of frequency stability, at ultrahigh frequencies, may be achieved with the aid of this cavity as the frequency-controlling ele- 'ment of the vacuum-tube oscillator, much in the same way as the frequency control of an oscillator is effected with the aid of a piezo-electric crystal. To minimize changes in frequency with temperature, the circuit element may be located in a constant-temperature box, or the construction and materials of the element may be such that the change in its physical dimensions with temperature shall be very small.

The invention is not restricted to use with the exciting rod 33, or 54. In Figs. 6 and 13, for example, these exciting rods are replaced by an exciting rod 12 that is connected with parallelwire conductors 13. In other respects, the terminal device shown in Fig. 6 is substantially the same as that of Figs. 1 and 2. In Fig. 13, the dimension of the shell I13 that is parallel to the exciting rod 12 is substantially parallel to the electric lines of force of the oscillatory waves within the cavity.

A modified terminal device possessing marked resonant properties and adapted for use as a sender or receiver is illustrated in Fig. '1. The hollow pipe 43 is there shown opening into the cavity provided by a closed metal cylindrical chamber 40, to the lower end of which an outer tubular conductor 4| is integrally secured, con centrically therewith. A conducting rod 42, disposed axially of the tubes 4| and 40, is extended into the pipe or tube 40 to constitute the exciting rod. The tube 4| and the rod 42 are shown con- 1 and 2.

The exciting rod 42 may be of the same type as I described above in connection with the exciting rods 33, 58 and 64. It may, however, be of the same type as the rod 12 of Figs. 6 and 13, as illustrated at 45 in Fig.8. In this Fig. 8, the exciting rod 45 is shown similarly disposed within and axially of the cylinder 45 into which the hollow pipe 44 opens, and is connected, near its center, to the parallel-wire system 41, corresponding to the parallel-wire system 13 of Figs. 6 and 13. The wires 41 are shown extending into the cylinder 46 through an opening 9 at the side of the cylinder 45 opposite to the pipe 44.

The exciting elements 42 and 45 of Figs. 7 and 8 are adapted for the propagation of transverse waves into the hollow pipes 43 and 44, respectively. The exciting rod may be disposed at right angles to the hollow pipe 43 or 44, and to the axis of the cylindrical cavity 40 or 46 of Figs. 7 and 8, as illustrated at 25 in Fig. 9. The exciting rod 25 happens to be shown as the inner element of a coaxial line the outer element of which is constituted of a tube 23 that joins the' cylindrical cavity 40 at right angles thereto, in the same manner as described above in connection with Figs. 2, 4, 5 and 12. The exciting rod 25 may, however, be disposed at other angles to the cylindrical cavity 40, and it may be of the type illustrated at 45 and 42.

The conductors before described, such as the conductors 3 and 52, may represent either output terminal conductors or input terminal.conductors of suitable transmitting apparatus at the transmitting end, or receiving apparatus at the receiving end, of a hollow pipe. The same terminal devices, such as the terminal devices 58, 6|, to which these conductors are connected, may

be used for delivery of the energy in both directions. Except for questions of insulation and of impedance of the bi-conductor circuit, the terminal device for receiving may be the same as that for sending; for. as the'operation is entirely reversible, any device that will radiate waves through the hollow pipe will be equally effective in picking them up from the hollow pipe. This novel circuit element may, therefore, be used both for sending and receiving. Modulated highfrequency energy may be supplied to a suitable hollow-pipe system, in the case of the transmitting apparatus, and may be taken from the hollow-pipe system, in the case of the receiving apparatus. In the case of the receiving apparatus, the signal comprising the intelligence may be recovered by demodulation. In all such cases, the pipe 43 or 44 may constitute a uni-conductor system, connected at its sending or receiving end to the bi-conductor system 3, 62, the energy being transmitted through the inside or the interior of the hollow cavity of the present invention.

By locating within a hollow-pipe terminal device, say of the type shown in Fig. 12, a suitable grid 24, a chamber may be formed between the walls of the pipe 63, the grid 24 and the plunger 59. The grid is shown as comprising radial wires, but other shapes may also be employed. A parallel-conductor grid is appropriate for use with waves of the transverse type and the radial-wire grid for use with waves of the longitudinal type.

Some of the energy in a wave transmitted through the tube and impinging on the grid 24 will be reflected back into the chamber and some will pass through the grid into the chamber 63 on the side opposite to that exposed to the impinging wave. The amount reflected and the amount let through will depend upon the nature of the grid and on the orientation of the grid with respect to the plane of polarization of the wave, or whatever may correspond to the wave. This chamber may be inserted into a hollowpipe system, connections being made, for example, at 23, or at any other desired point of the chamber. If desired, a further connection or connections may be made to this chamber as, for example, by means of the bi-conductor connection 65, 66. Interconnection may thus be effected between a hollow-pipe system connected at 23 and the bi-conductor system 65, 66 by means of a novel type of terminal device,

In Fig. 11, the rod l2! may preferably be given such shape and length as to coincide substantially with a line of electric field intensity of the standing waves set up within the cavity. This shape will depend on the configuration of the cavity and on the frequency of the oscillations.

The cavity within the shell may be considered to have certain natural modes of oscillation, with corresponding natural frequencies of oscillation. These modes and frequencies are determined by the size, shape and electrical characteristics of the cavity. By so shaping and dimensioning the cavity that one of its natural frequencies, say its fundamental frequency, coincides with the operating frequency of the apparatus, the resonance property is made use of to a very complete extent. At a fundamental frequency, for example, the cavity behaves much in the same way as a parallel-resonant circuit. By providing a twoconductor electrical connection with the cavity, the highly-resonant low-loss properties of'closed cavities may be used in conventional circuits, according to the present invention; by providing a uni-conductor connection with the cavity, these What is claimed is:

1. A high-frequency low-loss impedance ele-' ment comprising a substantially closed conducting chamber provided with an opening, the size of said opening being adapted to reduce radiation losses from said chamber substantially to a minimum, and connecting means at said opening adapted to connect said impedance element to a high-frequency circuit in operative relationship, said connecting means guiding electromagnetic energy with low loss between the chamber and said circuit.

2. A high-frequency low-loss impedance element as defined in claim 1 in which only a single opening is provided in the chamber in order that the chamber may constitute a self-impedance.

3. A high-frequency low-loss impedance element as defined in claim 1 in which two openings are provided in the chamber in order that the chamber may constitute a mutual impedance.

4. A high-frequency low-loss impedance element as defined in claim 1 in which the highfrequency circuit comprises hollow-pipe waveguide means, said hollow-pipe wave-guide means having transverse dimensions of magnitude such as to permit transmission of waves of the said high frequency.

5. A high-frequency low-loss impedance element as defined in claim 1 in which the highfrequency circuit is a multiple-conductor circuit.

6. A high-frequency low-loss impedance element as defined in claim 1 in which two openings are provided in the chamber in order that the chamber may constitute a mutual impedance, the

. necting means comprises a terminal device.

8. A high-frequency low-loss impedance element as defined in claim 1 in which the connecting means comprises a conducting element.

9. A high-frequency low-loss impedance element as defined in claim 1 in which the connecting means comprises a conducting pipe connected to the opening and a conducting rod disposed substantially axially of the pipe.

10. A high-frequency low-loss impedance ele ment as defined in claim 1 in which a low-loss dielectric medium is'contained in the chamber.

11. A high-frequency low-loss impedance element as defined in claim 1 in which a gas is contained in the chamber.

12. A high-frequency low-loss impedance ele ment as defined in claim 1 in which the chamber is evacuated.

13. A high-frequency low-loss impedance element as defined in claim 1 in which the chamber is bounded by a surface of revolution.

14. Ahigh-frequency low-loss impedance element as defined in claim 1 in which the chamber is adjustable to adjust the impedance.

15. A high-frequency low-loss impedance element as defined in claim 1 in which the chamber is resonant.

16. A high-frequency low-loss impedance element as defined in claim 1 in which the chamber is resonant and means for adjusting the resonant frequency.

17. A high-frequency low-loss impedance element as defined in claim 1 in which the chamber is resonant and hollow-pipe wave-guide means connected to the opening, said hollow-pipe waveguide means having transverse dimensions of magnitude such as to permit transmission of waves of the said high frequency.

18. A high-frequency low-loss impedanceelement as defined in claim 1 in which the chamber is resonant, means for setting up standing waves of resonant frequency in the chamber. and means,

ment as defined in claim 1 in which the connecting means comprises a conducting rod extending into the opening, one end of the conducting rod being connected to the chamber.

21. A high-frequency low-loss impedance element as defined in claim 1 in which the connecting means comprises a conducting rod extending into the opening, the conducting rod having a looped end connected to the chamber.

22. A circuit element comprising a hollow resonant conducting chamber providing a resonant cavity and having an axis, and a conducting rod disposed in the chamber substantially at right angles to the axis to constitute an exciting element for setting up standing waves of the resonant frequency in the cavity.

23. A circuit element comprising a hollow resonant conducting pipe providing a resonant cavity, a conducting tube connected to the pipe substantially at right angles thereto, and a conductor disposed in the tube and the pipe substantially at right angles to the axis of the pipe to constitute an exciting element for setting up standing waves of the resonant frequency in the cavity.

24. A circuit element comprising a hollow resonant conducting chamber providing a resonant cavity and having an axis, a conducting end aasauo plate closing one end of the chamber and provided with an opening disposed substantially along the axis of the chamber, a conducting tube outside the chamber and connected to the end plate along the opening, a conducting rod extending through the opening into the chamber substantially axially of the chamber to constitute an exciting element for setting up standing waves of the resonant frequency in the cavity, and means for electrically connecting the rod and the tube with an electric circuit for exciting the rod.

25. An electric system comprising a hollow resonant conducting chamber, a conducting tube connected to the chamber. a conducting rod disposed in the tube and extending into the chamber, vacuum-tube apparatus, and means connecting the vacuum-tube apparatus to the rod and the tube.

26. A circuit element comprising a hollow resonant conducting chamber having an axis, a

. conducting tube connected to the chamber substantially at right angles to the axis of the chamber, a conducting rod disposed in the tube and extending into the chamber substantially at right angles to the axis of the chamber, means for connecting one end of the rod to the chamher, and means for electrically connecting the rod and the chamber with an electric circuit.

27. A circuit element comprising a hollow conducting chamber providing a resonant cavity, a hollow conducting pipe opening into the chamber, a conducting rod disposed in the pipe and extending into the chamber to constitute an exciting element for setting up standing waves of resonant frequency in the cavity, means for connecting the rod with outside exciting apparatus for exciting the rod, the circuit element being provided with a hollow extension or extensions, and one or moreadjustable conducting to a critical wave-frequency below the resonant frequency.

WILMER L. BARROW. 

